Testing Sodium Silicate to Determine Optimal Baking Temperature and Sugar Content

Discussion in 'Sand Casting' started by Melterskelter, Jun 25, 2019.

  1. Melterskelter

    Melterskelter Silver

    I have been wondering how much difference sugar content and baking temperature may make in sodium-silicate-bound cores. Typically I have been using Tom Corbett’s recommendation for making NaSi cores in which he recommends mixing sand with 5% binder. I know the sugar addition results in a core that is easy to remove from cast iron castings after shakeout and not using sugar results in a concrete-like core that is, seriously, nearly impossible to remove in some cases from an iron casting. But, the questions I want to answer are:

    1) How much does the sugar weaken the core prior to casting? (I suspect it weakens the core significantly precast.)
    2) How much difference in precasting strength does varying the sugar content make.
    3) How much does baking temperature affect precasting strength of various sugar additives.
    (There May be more questions to answer like “how does baking duration affect precast strength?”

    He recommends using Sodium Silicate RU + 15%water + 15% table sugar as the binder.
    He suggests adding about 5% by weight binder to clean sand. I am using olivine 100 mesh.

    So, today I mixed up 3 batches of silicate bound sand varying the sugar content from 0, 5, and 10 percent.
    I intend to bake the core I made at varying temps as well from a high of 200F to down around 120F all for 90 mins. As trends develop I will further explore concentration of binder, sugar content etc. Here are pics of the cores with end stamps corresponding to sugar %.

    55457DAD-7E8A-44D5-8058-3FA9C0FAF1BE.jpeg FDF056F7-7CDC-4EF9-B3F8-D7AA8A951309.jpeg

    Getting real answers is just plain hard work. If anyone already has some answers to these questions based on personal observation or formal testing I’d like to hear about it. I will put up data as I get it.

    I intend to support the cores by blocking up each end and loading them in the center until each breaks as a first pass at strength testing.

    dtsh likes this.
  2. Melterskelter

    Melterskelter Silver

    I can see this thread has captured the collective imagination of the forum----well maybe not. ;-)

    I do have some data now.

    As suspected, cooking the core seems to increase its strength.

    Here is the setup:
    The span between upright arms of the cradle that support the test bar is 2.75"
    The diameter of the test bars is .92"

    CoreStrgthTest (2).JPG

    And the result after pouring 11 pounds of sand into the bucket:

    CoreStrgthTest (1).JPG

    So far it looks like the 7 beam tests indicate:
    1) The more sugar is incorporated into the binder the weaker the core
    2) Baking the core strengthens it.
    Data so far:
    % Sugar Cook temp Break Load Pounds-oz

    0 ............No Bake............11-9
    (5............No Bake............ 2-12)*
    (5............No Bake............3-3)*
    5........... .No Bake............6-4
    10...........No Bake............4-13

    5............. 160F.................6-11
    10............160F................ 3

    0............ 200F............17-2
    5........... .200F............11-0


    0........ ....350F............13-0

    * The measurements marked with an asterisk and in parenthesis are in doubt with a methodological error suspected.

    All bake times are 90 min with the test cyclinder allowed to cool to room temp prior to testing

    I repeated the 5% No Bake test as the result seems anomalous. But it seemed to repeat. Maybe I messed u on that batch. I am currently baking to 350 a couple cores. I do not expect to get a large number of data points. But it is interesting to actually have some numbers to go with what were previously just impressions. I do expect to do enough tests to have a pretty good idea of what the relationship to bake temp and sugar content are. Then I will need to do some testing to see what the minimal amount of sugar added that still allows easy removal of core sand.

    This all relates to my attempting to cast the long thin hollow triangular prism talked about in another thread.


    Edit data points added 6-27-19 More samles are in the oven.
    Edit: Today (6-29) I added some 160F data. That may be my last Sodium Silicate testing. I am still considering oil binders.
    Last edited: Jun 29, 2019
  3. Peedee

    Peedee Silver

    *I'm interested (but quietly watching your results)

    I wonder, without adding to your data, at what point does off-gassing become a problem with an increased amount of sugar in the core or does baking resolve some of this?
  4. oldironfarmer

    oldironfarmer Silver

    This is great!

    Of course the more tests the better.

    I seem to have extremely variable results with N-grade but some of it is quite acceptable. I really need to figure out how to make consistent cores.

    Thanks for starting down this road.
  5. Melterskelter

    Melterskelter Silver

    I have not considered sugar to be a source of off-gassing. I think it is unlikely to have much if any volatile component below caramelizing temps. It has no evident adverse effect on casting quality at 15% composition of the binder (that would be just under 1% of the content of the silicate bound sand. ). In fact casting finish and detail rendition from the silicate bound sand is excellent. I am just trying to see if what is giving good results can be made to be stronger so that core molding structural limits can be pushed without sacrifice of shakeout properties and detail rendition.

    I’ll be baking some more today... I wish chocolate chips could somehow be justified in the mix. ;-)

  6. Jammer

    Jammer Silver Banner Member

    The other half of this will be how easy it is to remove after casting and will it have a tendency to have a blow out. My homemade SS is very weak unbaked and very hard baked, and almost like concrete after casting with aluminum.
  7. Melterskelter

    Melterskelter Silver

    I have addressed this hardness issue in other threads. Sugar is the answer. Tom Cobett has nice monograph online talking about this and it from him tha I got the idea.

  8. Melterskelter

    Melterskelter Silver

    Here is a video on sample prep for this test series. I wanted to add a caption saying the tube had been sprayed inside with silicone spray to make separation of the sand from the tube easy. But I do not see where captions can be added within YouTube. Sorry.

    The debris from completed tests:


    The general setup:


    Last edited: Jun 26, 2019
    Mark's castings likes this.
  9. Chazza

    Chazza Copper

    Nice work Denis!

    I am very interested and appreciate the time and results that you have shared with us – thank you!

    Cheers Charlie

    PS Brilliant film as well!
  10. Melterskelter

    Melterskelter Silver

    Thank you all for the various encouraging remarks above.
    I updated the dataset with a few more points this AM.
    I have some 5 and 10% bars in the oven at 275 right now.

    Last edited: Jun 27, 2019
  11. Melterskelter

    Melterskelter Silver

    I think I have enough data now posted above to conclude:

    1) That somewhere between no bake and 200 degrees results in maximum strength of a sodium silicate core
    2) The more sugar added the weaker the core.

    Perhaps I will try curing a couple more cores this time at 160 just to see if there is any indication of significantly more or less strength at that temp.


    Now I am curious as to the relative strength of a core made with linseed oil. So, I am asking those who have some experience with linseed oil to please advise me on their methods of putting together a strong but easily removed linseed oil core.

    I can use the same tube for the NaSi core to make a few cores with linseed and should be able to test their beam strength as well. that will help me answer a nagging question as to which is stronger.

    Tobho Mott likes this.
  12. Chazza

    Chazza Copper

    A question about your Sodium Silicate Denis – is it in solution with water?

    I can buy it here as solution, presumably with water, 42%,

    Cheers Charlie
  13. Melterskelter

    Melterskelter Silver

    I buy solution. NaSi composition is a bit more than simple concentration. Tom Corbett has a good paper worth reading. He tells you what you need to know about silicate. From stories of trouble with other forms of silicate I have heard, I would really try to get RU.


    Chazza likes this.
  14. oldironfarmer

    oldironfarmer Silver

    Does anybody have a good mail order source for RU? My local refractory company does not carry any.
  15. Melterskelter

    Melterskelter Silver

  16. Chazza

    Chazza Copper

    Thanks Denis,
    Yes I have Tom's treatise; the biggest hassle for me over here, is finding anywhere that sells foundry supplies and actually replies to my queries,

    Cheers Charlie
  17. Melterskelter

    Melterskelter Silver

    Final silicate test data added today. Two entries for 160F
  18. ESC

    ESC Silver Banner Member

    My recipe for linseed oil bonded cores is:
    40:1 sand to oil. I mix 900ml of core sand with 100ml of my petrobond sand and a couple tablespoons of flour for greenstength. After the dry is mixed I drizzle in 25ml of boiled linseed oil and 10ml of kerosene.
    Core plates are a necessity for baking the cores, but any sheet aluminum will work as long as it stays flat.
    I bake the cores at 350F for an hour or more depending on the thickness to make sure the core is fully dried. I use flour paste to glue cores together and rebake at 150F . They are durable and can be handled and shaped with a Dremel grinder after baking. They can be returned to the oven for more time if they are slightly soft. They have a long shelf life if they are kept dry.
    Venting of the core itself and the mold is critical due to residual oil volatilizing.
    Last edited: Jun 30, 2019
    Melterskelter likes this.


    Hill and Griffith Company, Corosil GU Sodium Silicate. They are based in Cincinnati, but they also have an Indianapolis location, so I called to inquired about the RU formula I was looking for and they told me that their Corosil GU is in fact RU. They have it in stock in Indianapolis and it's no problem for anyone to drop by the Indy store to buy it. A 5-gallon pail weighs 60# and they charge .97 cents per pound for it. $58.20 for 5-gallon
  20. Melterskelter

    Melterskelter Silver

    Good to know another source and good to have a litle more information on the proprietary naming of products. The various names for the same chemical entitiy adds to the fun...


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